Did you also install the (legacy) firewire system driver? That is not included in the Windows 8 or 10 builds and must be downloaded separately from Microsoft. It was built into Windows 7. The only stable 1394 driver for the MR816, IMHO. It fixed the problems I was having in W 10. The link below says its for Windows 8, but it also works in Windows 10.
BTW, video card drivers play a big role in this, too.